Conventional spray bars commonly comprise an elongated block-like header that supports a plurality of spray nozzles in side-by-side relation, with the header block being formed with passageways that extend along the length of the header block for communicating liquid, air, or other fluids to the nozzles and to actuating mechanisms for the nozzles. Such conventional spray bars had been subject to various manufacturing and performance drawbacks.
At the outset, the elongated liquid and air passages in the header block typically are formed by gun drilling, a well-known machining procedure for forming relatively long bores such as gun barrel bores. Gun drilling is tedious and expensive. Moreover, as greater numbers of passages are required in the header block, such as when the header block must also supply air for both liquid atomization and nozzle actuation, the multiplicity of passages can become complex, limiting the number of spray nozzles or their mode of operation. This can limit the width of the liquid spray curtain, or the ability to selectively control the spray curtain width.
Conventional spray bars also are not susceptible to easy or thorough cleaning, such as required for sterile or uncontaminated spraying food substances and pharmaceuticals. Furthermore, by reason of inaccessibility into gun-drilled holes of the header block, the fluid passages are not susceptible to electropolishing as required for effective cleaning.
Performance problems also exist with existing spray bars, particularly when spraying highly viscous substances, such as liquid chocolate. Pressure losses occurring along the length of the passages within the header block result in the supply liquid being communicated to differently located nozzles at different inlet pressures. The resulting non-uniform spray discharge from the individual nozzles, in turn, results in non-uniform product application.